1. Field of the Invention
The present invention relates to an imaging device incorporated into electronic equipment such as a digital still/video camera, a cellular phone, and so on. Especially, it relates to a signal process associated with color reproduction.
2. Description of the Related Art
In an imaging device, a primary color filter such as an R, G, and B color filter or a complementary color filter such as a Ye, CY, Mg, and G color filter is arranged on a photo-sensitive area of an image sensor. In the color filter, color elements are arranged in a checkered configuration such that the color elements are opposite pixels arranged in the photo sensitive area. Light, reflected off an object, passes through the color filter so that image-pixel signals, which are composed of color signals corresponding to the color elements, are generated. The image-pixel signals are subjected to a color conversion process, namely, a matrix computation which produces image signals dependent upon a given standard color space defined through the colorimetry. Consequently, video signals such as NTSC signals are output to a peripheral apparatus such as a monitor.
In a digital camera, various arrangements of the color elements and various color-conversion processes have been attempted in order to accurately reproduce an objective color as accurately as possible, namely, to reproduce the objective colors so as to match those perceived in real life as closely as possible. For example, a color element G′, which has a relative spectral transmission property or characteristic close to that of a given Green color element (G), may be arranged in the color filter in place of the Green color element G, in order to correct for a biased red color signal. In a different approach, the color filter is composed of four color elements, R, G, B, plus an additional color element that has a different spectral transmission property. In this case, R, G, and B primary color signals, corresponding to tristimulus values, are generated by a 4×3 matrix computation. The four color elements reproduce an objective color while reducing noise.
However, since the relative spectral-transmission properties of color filter do not necessarily coincide with the visual relative response property, an adequate reproduction of the objective color is difficult.